Various mechanisms at layers 2 and 3 can provide protection against network failures. Some of these mechanisms (e.g., multiprotocol label switching (MPLS) fast reroute (FRR)) may be relatively fast, and may guarantee a short duration from failure detection to diversion of traffic onto an alternate route. Other mechanisms, such as interior gateway protocol (IGP) routing protocols, such as open shortest path first (OSPF), can take longer to converge. Newer protocols, such as Internet protocol (IP) FRR are also being implemented.
In such conventional approaches, the switching criterion may be a failure of a signal at an incoming synchronous optical networking (SONET) or other interface. These failures may typically be “hard” failures, such as loss of signal. While protection could be triggered by a degradation of the signal, these degradations may be rare when a router interface is connected to a dense wavelength-division multiplexing (DWDM) transport network because the signal is likely to be corrected via a transponder, as long as the error rate is below a certain level. Once the error rate exceeds a given level, the signal can become corrupt, and result in a traffic hit while the router switches to a protection path.